IDL compiler: Rename 'args' to 'info', remove |callback_info| and |isolate| as possible

Python side to 'args' => 'info' CL.
This also allows significant simplification, since now |callback_info|
is always 'info', and |isolate| is almost always 'info.GetIsolate()'.

2 questions:
1. Should assume |isolate| == 'info.GetIsolate()' in V8_VALUE_TO_CPP_VALUE?
In CPP_VALUE_TO_V8_VALUE, we need to have an {isolate} parameter b/c
callback interfaces have |isolate| == 'isolate' instead,
but for attributes and methods (which are all that use V8 -> C++ for)
this assumption is true.

2. Style-wise, we could:
a. use {isolate} in string templates and pass isolate='info.GetIsolate()'
(which might be clearer),
b. inline 'info.GetIsolate()' (to be explicit), which is what I've done now.

Ref:
Rename |args| to |info| in V8 bindings
https://codereview.chromium.org/54283002/

BUG=239771
NOTRY=true

Review URL: https://codereview.chromium.org/55163004

git-svn-id: svn://svn.chromium.org/blink/trunk@161128 bbb929c8-8fbe-4397-9dbb-9b2b20218538